The Afghan authorities have arrested 18 people in Kabul after foiling plans for an apparent mass suicide attack, intelligence officials say.
They told the BBC that 11 suicide jackets had been seized inside the ministry of defence.
The officials say the attacks would have caused significant loss of life. Some of those arrested are reported to Afghan National Army soldiers.
The Afghan Ministry of Defence dismissed the report as "rumours".
Dawlat Wazeri, the ministry's deputy spokesman, told the BBC that no would-be bombers had been detained or suicide vests seized inside the ministry.
"These are just rumours and now we are working on finding the men who have provided these rumours to the media," he said.
The BBC's Bilal Sarwary in Kabul says it appears that, officially, the Afghan authorities want to play down a major security lapse that is highly embarrassing for the government.
The reliability of Afghan security personnel is in the spotlight after a string of deadly attacks by gunmen wearing Afghan National Army dress on their Nato counterparts in recent weeks.
Intelligence officials told our correspondent that the jackets had been seized on Monday afternoon from three separate rooms around a ministry car park, less than a kilometre from the presidential palace. Several people were arrested inside the ministry's first security belt, they said.
Six soldiers were arrested at the time - initial reports suggested they were armed and prepared to attack.
It appears the jackets were intended to be detonated on buses transporting staff to and from work. Eleven buses carrying 1,100 personnel were due to set off just 45 minutes after the arrests were made, our correspondent reports.
Another 12 people were arrested on Tuesday and more arrests could follow, intelligence and security officials told the BBC.
Our correspondent says the problem of attacks by rogue soldiers and Taliban infiltrators has plagued the Afghan police and army for several years.
The arrests came as people wearing the uniforms of Afghan security forces killed one US and two British soldiers in separate incidents on Monday, in Paktika province and Lashkar Gah in Helmand respectively.
Attacks on US and Nato forces have increased since the inadvertent burning of Korans by US troops in February and the massacre of Afghan civilians by a US a soldier on 11 March.
Nato is due to withdraw combat forces from the country by 2014. Meanwhile efforts are being made to negotiate with the Taliban and to build up the Afghan security forces so they can assume full security control once Nato combat troops depart.
The Taliban pulled out of the talks earlier this month, accusing the US of being "erratic and vague" in its dealings with them.